This invention relates to a vapor phase process for the disproportionation and rearrangement of chlorofluoromethanes with carbon tetrachloride to yield trichloromonofluoromethane, dichlorodifluoromethane, and chloroform, using an activated alumina and magnesia catalyst.
Generally, fluorinated alkanes are produced commercially by reacting hydrogen fluoride with chloroalkanes in the presence of a catalyst: Daudt et al., U.S. Pat. Nos. 2,005,705 and 2,005,708. The fluorination reaction may be represented by the following equation using chloroform as the illustrative haloalkane: ##STR1## wherein x is 1 to 3. A mixture of products, dichloromonofluoromethane (CHCl.sub.2 F), monochlorodifluoromethane (CHClF.sub.2), and trifluoromethane (CHF.sub.3), is usually obtained from this reaction. The amount of each reactant which is produced depends on the process feed ratios and the reaction conditions. However, it is not generally possible to completely avoid the production of undesirable products through control of process parameters. For example, the production of CHF.sub.3 frequently exceeds demand and the fluorine values in the CHF.sub.3 are usually wasted because no economical process is known for their recovery.
JP Patent No. 60-6928 describes a catalyst for disproportionation of fluorine-containing halocarbons. The catalyst consists of chromium oxide, magnesium oxide, and aluminum oxide and contains mostly aluminum oxide based on the weight of total oxides. U.S. Pat. Nos. 3,087,976 and 3,793,229 disclose the use of an alumina catalyst activated by reacting with hydrogen fluoride and a lower fluorocarbon, respectively. Use of these known catalysts to disproportionate trifluoromethane led to the formation of monochlorotrifluoromethane, an even less desirable product.
It is therefore an object of the present invention to recover fluorine values by selective disproportionation of chlorofluoromethanes to obtain the commercially significant products, trichloromonofluoromethane, dichlorodifluoromethane, and chloroform. The chloroform which is also produced from this reaction can be used for other purposes, e.g., recycled to the primary fluorination reaction above.